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Add fast path to json string encoding #135336

Description

@nineteendo

Feature or enhancement

Proposal:

Most JSON strings consist solely of ASCII characters that don’t require escaping, so adding a fast path for those would make a big difference. In these cases, we can avoid allocating a new string by writing the original string directly:

PyUnicodeWriter_WriteChar(writer, '"')
PyUnicodeWriter_WriteStr(writer, pystr) // original string
PyUnicodeWriter_WriteChar(writer, '"')

Benchmarks have shown that this roughly 2.2x faster, see PR.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

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Activity

  1. added a commit that references this issue on Aug 7, 2025
  2. added a commit that references this issue on Aug 19, 2025
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